RESPIRATION 



25 



This proves very clearly that carbon dioxide is pro- 

 duced by the living seeds, flowers or leaves. 



Fig. 3 shows another ap- 

 paratus by which we may see 

 that not only is carbon dioxide 

 given out, but almost (though 

 not necessarily quite) the same 

 volume of oxygen is absorbed. 

 C, A and B are three tubes, 

 broader at one end than at the 

 other. We stand the narrower 

 ends in water and put a few 

 pea or bean seeds that have 

 been soaked in water, or some 

 opening flower-buds, in the 

 broad ends of A and B, but 

 in C, any dead seeds or buds, 

 resting them on a little cotton- 

 wool to prevent their falling 

 down into the water. In the 

 FIG. 3 tubes C and A we put a short 



test-tube containing a stick of caustic potash and then 

 close both tubes tightly with good corks. After a 

 little while in a few minutes if the seeds had first 

 been soaked for a day the water begins to rise in 

 the tube A, while that in B may fall a little and then 

 remain stationary and in C it does not alter at all. 

 In A the water continues to rise, and will do so (if 

 there is enough caustic potash in the test-tube) till about 

 one-fifth of the whole tube is full of water. But if it 

 be left more than two days, the seeds will begin to 

 ferment and go Votten, and the water to fall down again. 



